Liquid paint and coating manufacturers produce either water-based or solvent-based (or both). This section will cover formulation, typical manufacturing materials, processes and wastes of water and solvent-based paint and coating production.

Formulation/Composition

Paint formulators design paints and coatings for hundreds of different specific end uses and different attributes. The manufacturing process is also designed to yield the desired properties of the final product, through very strict control of mixing times, mixing speeds, when to add different ingredients, and other specifications.

Liquid-applied paints typically consist of the following components, with the binder (or resin) making up the majority of the paint formulation as shown in the figure below.

Binders (or resins) provide the vehicle which helps the pigment stick to the applied surface and form a film. The binder influences properties such as gloss, durability, flexibility, and toughness. Synthetic or natural binders include alkyds, acrylics, vinyl-acrylics, vinyl acetate/ethylene, polyurethanes, polyesters, melamine resins, epoxy, or oils.

Solvents are the carriers or thinners, which keep the paint in liquid form until applied and cured. They dissolve the polymer and also adjust the viscosity of the paint. Solvents are volatile and therefore do not remain part of the dried paint film. Solvents include water (for water-based paints), mineral spirits and ‘odorless’ mineral spirits (a mixture of aliphatic hydrocarbons), naphtha, lacquer thinner (a blend of different solvent types), or denatured ethyl alcohol, and aromatics, such as xylene and toluene. All of the aforementioned solvent products, aside from water, are volatile organic compounds (VOC)s and are subject to air and hazardous waste regulations.

The paint production process typically involves most or all of these steps, but differs slightly for latex or water-based manufacturing.

Initial filtration of raw materials ensures purity. The most common filters are bags or cartridges that allow particles of certain types or sizes to pass through the filtration media. Suspended particles, which could harm the consistency of the final product, are filtered out.

Mixing and Milling – High speed mixers combine water, thickener, and stabilizers and dry pigments and pigment extenders in a vat to create the paint base. Ingredients are added in quantities and times per very specific formulations. Some pigments require more intensive dispersion processes than others. Ball mills, for example, rotate golf-ball sized porcelain balls to break up agglomerates. Bead or sand mills use smaller particles (beads or sand) to agitate pigments.

Other additives may be incorporated at this time, or in the blending process.

Mixing machines rotate serrated discs at up to about 1000 rpm to. Larger machines typically use rotating scraper blades to remove material from the sides of the mill-base vat.

Blending –The mill-base mixture is pumped to a larger vat containing the balance of the resin material and a thinner (water, or a solvent. or blended solvents) are added. The mixture may be stirred for several hours, as prescribed by the formulation design.

Post-blending Filtration - Filtering the blended paint prevents large pigment particles and coagulants from entering the final product. Different types and qualities of paint require different types of filters. As with initial filtration of raw materials, bags and cartridges are most common, Self-cleaning or reusable filters are available.

Fillingand Packaging –When processing is complete and batch of paint passed quality tests, the paint is transferred to a hopper for automated filling of cans or buckets. Paint may be packaged in metal cans or plastic buckets (as large as five gallons). Labeling, either adhesive-applied paper labels, or direct printing on the packaging, is usually completed prior to filling.

Latex is around 60% water, so metal cans must be internally coated to prevent rust, prior to filling.

Filling, weight-checking, sealing full containers, and attaching handles to the containers, are automated.

Clean-Up - Methods vary greatly. Cleaning chemicals, water, and solvents can be used, depending on the type of paint, and whether it has dried onto tank walls. Scrubbing or polishing tanks manually, with sanders or scrubbers, is also a common industry practice.

Wastes and Emissions

The main waste streams in paint production are indoor and outdoor air emissions, wastewater, and solid or liquid wastes. Solvent-based paint production generates significantly more hazardous waste than water-based.

When the raw materials used in manufacturing process contain VOCs (e.g., most solvents), and/or heavy metals, most of the waste by-products of the process, such as off-specification paint that is unusable, or material from the cleanup of equipment, the waste cannot be placed in the municipal waste stream. If the presence of VOCs and heavy metals in the resulting waste stream exceeds allowable levels for municipal waste, as determined by regulatory standards, the paint and coatings manufacturer is required to handle the waste as a hazardous or dangerous waste.

Air emissions released to outdoors occur from gases created during the manufacturing process and evaporative losses of volatile products. Indoor air emissions occur from evaporative losses and releases of volatiles, and fugitive dust from handling and milling of powdered raw materials.

The Western Sustainability and Pollution Prevention Network (WSPPN) is a cooperative alliance of pollution prevention (P2) programs throughout EPA Region 9 (Arizona, California, Hawaii, Nevada, Trust Territories, and Tribal Lands). The network serves as a technical resource for regional P2 issues through researching, consolidating, and disseminating P2 information. WSPPN was established in 1997 and is run as a service provided by The Business Environmental Program (BEP) at the University of Nevada, Reno.